1. Field of the Invention
The present invention relates to a nano-gap electrode device having a nano-gap with a width of several nanometers or less between two electrodes and, more particularly, to a method for manufacturing a nano-gap electrode device that the nano-gap position and width can be adjusted readily and a plurality of nano-gaps can be fabricated.
2. Discussion of Related Art
As information and communication technology have been developed, a quantity of transferable information increases geometrically. As a result, integrity for processing the large quantity of information in a semiconductor device has been enhanced continuously. In a prior art, the integrity of the semiconductor device has been improved by a top-down method that a size and a line width of the device are reduced through an enhancement of a resolving power in a photolithography process. However, it is not applicable for a practical use since the process thereof is difficult and it is required a high cost. Thus, a nano molecular device has been developed so as to solve the aforementioned problems and improve an economical efficiency. Recently, a nano molecular device fabricated by a bottom-up technology has been proposed.
The molecular device is such a device that applies electronic transport through molecules each having a length of several nm or less, contrary to a silicon based semiconductor device of a prior art. The molecular device has been considered as a next generation technology since a high-integrated high-speed circuit can be implanted with low costs. The molecular device requires external electrodes connected to both sides of the molecule for an electrical characteristic evaluation. For this, it is necessary to implant electrode devices that are spaced apart from each other across a nano-gap corresponding to a molecular length of several nm or less.
Conventionally, the nano-gap electrode device has been manufactured by a method that a certain portion of a metal line is broken by mechanical stress or electromigration, or a method that a gap having a width of hundreds of nm is formed first by electron beam lithography, and then an electrode material is further deposited on surfaces of the two electrodes by means of an electrochemical deposition method to thereby narrow the width of the gap. However, the methods as mentioned above have demerits that the processes thereof are complex and the precise control of the gap position and width is difficult. As a result, reproducibility and reliability get deteriorated. In addition, it is not applicable for the fabrication of integrated molecular device circuits since a plurality of nano-gap devices each having the same shape and width cannot be implanted at the same time.
FIGS. 1A to 1E are typical views for explaining a method for manufacturing a nano-gap electrode device according to a prior art, in which a metal line is broken by mechanical stress. And, FIGS. 1B to 1E are enlarged views of A portion shown in FIG. 1A.
Referring to FIG. 1A, a metal line 12 is formed with a gold (Au) and etc. on a substrate 11 that is covered with an insulation film and composed of a silicon and so on, and then a central portion of the metal line 12 is dipped in a solution 13 including a certain molecular material. A configuration 14 is contacted with a bottom side of the substrate 11, where corresponds to the central portion of the metal line 12, and mechanical configurations 15 are contacted with an upper side of the substrate 11, at both sides of the metal line 12.
Referring to FIGS. 1B and 1C, if a mechanical stress is applied to the substrate 11 in an upper direction by raising the configuration 14 while the mechanical configurations 15 being fixed, the central portion of the substrate 11 comes to be bent upward by the applied stress.
Referring to FIG. 1D, a certain portion of the metal line 12 is broken, resulting in a gap 16 if bending of the substrate 11 becomes larger with an increase of the stress. A self-assembled monolayer (SAM) 17 is formed on surfaces of two facing metallic electrodes 12a and 12b across the gap 16.
Referring to FIG. 1E, the bent substrate 11 is flattened, so that the two metallic electrodes 12a and 12b come to be contacted each other again across the monolayer 17, if the lower configuration 14 goes down and is returned to an original position.
Therefore, an electric signal may be applied to the monolayer 17 through the two metallic electrodes 12a and 12b. 
As described above, the method for manufacturing the nano-gap electrode device of the conventional art, in which the metal line is broken by the mechanical stress, has demerits that the process thereof is complex and the precise control over the gap position and shape is difficult, so that reproducibility and reliability get deteriorated and a plurality of nano-gap electrode devices cannot be fabricated at the same time. In addition, it is difficult to apply to a fabrication of an integrated molecular device circuit, since the mechanical stress applied to a certain position affects the other regions of the periphery.
FIGS. 2A to 2C are typical views for explaining a method for manufacturing a nano-gap electrode device according to a prior art, in which the metal line is broken by electromigration.
Referring to FIG. 2A, a metal line 21 with a line width of several tens of nm to hundreds of nm is formed by using a conventional semiconductor process technology.
Referring to FIG. 2B, large quantity of currents 23 pass through the metal line 21 by applying a voltage through terminals 22 at both sides of the metal line 21.
Referring to FIG. 2C, atoms inside the metal line 21 come to move gradually due to an effect of electron flow when the currents pass through, as mentioned above. The aforementioned phenomenon is referred to as an electromigration, by which a certain portion of the metal line 21 is broken, resulting in a nano-gap 24 having a width of several nm. The method for manufacturing the nano-gap electrode device of the prior art, in which the metal line is broken by electromigration, has a merit that the process thereof is simple relatively. However, it has demerits that the precise control over the gap position, width, and shape is difficult, thereby reproducibility being deteriorated, and a plurality of nano-gap electrode devices cannot be fabricated at the same time.
FIGS. 3A and 3B are cross sectional views for explaining a method for manufacturing a nano-gap electrode device using electrochemical deposition method, according to a prior art;
Referring to FIG. 3A, two metallic electrode patterns 34 are formed on a semiconductor substrate 32 on which an insulation film 31 is formed, wherein the two metallic electrode patterns are spaced apart from each other across a predetermined gap 33. The metallic electrode patterns 34 may be formed by using a conventional semiconductor process technology such as electron beam lithography, and a width of the gap 33 may be about hundreds of nm.
Referring to FIG. 3B, an electric terminal (not shown) is connected to the metallic electrode pattern 34, and the whole substrate 32 including the metallic electrode patterns 34 are dipped in a certain electrolyte solution. Electrode layers 35 are deposited on surfaces of the metallic electrode patterns 34 if a voltage is applied to the metallic electrode patterns 34 through the electric terminal. The width of the gap becomes thin more and more as the thickness of the deposited electrode layers 35 become thicker. As a result, a nano-gap 36 is fabricated.
However, the method for manufacturing the electrode device using the electrochemical deposition in accordance with the prior art has demerits that the process thereof is complex, the precise control over the width of the nano-gap is difficult, and a plurality of the nano-gap electrode devices cannot be fabricated at the same time.